This research aims at making a novel class of dental materials that is radically different from all existing dental materials. Funded by NIH (R01-DE09848), such materials, which covalently and uniformly incorporate polymers into inorganic matrices at the molecular or nanometer scales, have been successfully synthesized via the sol-gel reactions. Curable thermally or photochemically, these molecular composite/hybrid materials exhibit tailored combinations of the hardness of inorganic glasses and the toughness of organic polymers. There is no macroscopic phase-separation in these materials so that the interface problems as exist in conventional dental composites are eliminated. In this proposal, basic studies are proposed for 3 key issues in the sol-gel chemistry of hybrid materials with low shrinkage, with base-catalyzed nanoparticle formation, and with nanophase generation in nonsurfactant-templated sol-gel process. Aided by the first two studies, several improved or radically new strategies are designed to achieve the goals of further reducing or eliminating the volume shrinkage and of shortening the reaction time for practical dental applications. Two independent major approaches, through methacrylate-modified oligomeric silica precursors and methacrylate-modified silica nanoparticles (less than 100 nm), are proposed for preparing simple, one pack, ready to use, photocurable, paste products. These products can be light-cured to afford novel polyacrylate-silica hybrid dental materials in seconds with lower or zero volume shrinkage. Depth of cure will be improved because the silica domain size is smaller than the wavelengths of UV or visible light. With the studies of the nonsurfactant-templated process, nanoporous chemical hybrid fillers for dental resins and the use of polymerizable templates are designed to yield nanostructured dental materials. In all new materials the polymer and silica components are uniformly dispersed and covalently bonded with each other at the molecular or nanometer scales. Hence, the mechanical properties, particularly the wear resistance and the surface smoothness of the materials should be superior over conventional dental composites. Elimination of the interface should also reduce or prevent water-sorption and microleakage. Success of this research will lead to new science and technologies of hybrid and nanostructured materials for practical dental applications.